Haktos the Unscarred

For spells with {X} in their mana costs, use the value chosen for X to determine the spell's mana value. If a card or permanent in any other zone has {X} in its mana cost, X is considered to be 0.

If Haktos can't attack for any reason (such as being tapped or having come under that player's control that turn), then it doesn't attack. If there's a cost associated with having it attack, you aren't forced to pay that cost, so it doesn't have to attack in that case either.

A number is chosen randomly for Haktos before it enters the battlefield. There's no point at which players can target it before it has gained the appropriate protection abilities.